How to Send Inventory to a 3PL: Inbound Receiving, ASNs, and the Mistakes That Cost You Weeks

To send inventory to a 3PL you submit an advance shipping notice (ASN), label every carton with the SKU and quantity inside, ship it to the receiving address on the appointment, and the warehouse counts it in and makes it sellable. That is the whole process in one sentence. The reason it goes wrong is almost never the shipping — it is unlabeled cartons, mixed SKUs in one box, and a missing ASN, which together turn a two-day receiving job into a two-week one while your stock sits unsellable on a dock.

This is the step most brands underestimate during onboarding. Here is how inbound actually works, what each document does, and the specific mistakes that cost the most time.

What is an ASN and why does it matter?

An advance shipping notice (ASN) is the heads-up you give your 3PL before inventory arrives. At minimum it tells them: what SKUs are coming, how many units of each, how many cartons or pallets, when it will arrive, and the carrier and tracking or BOL number.

The ASN is what turns receiving from discovery into verification. With one, the team knows what to expect and only has to confirm it. Without one, they have to open cartons, identify products, count, create records, and guess at your intent — which is slower and far more error-prone. Most receiving discrepancies trace back to a missing or wrong ASN.

How do you prepare inventory for a 3PL?

1. Get your SKUs and barcodes set first

Every sellable unit needs a scannable barcode that matches the SKU in your store and in the 3PL's system. If your products do not have barcodes, most 3PLs can apply them — but that is a billable per-unit service, so it is cheaper to have your manufacturer do it. Confirm the format your 3PL expects before your next production run.

2. One SKU per carton

This is the single highest-impact rule in inbound. A carton containing 48 units of one SKU can be received in one scan. A carton containing a mix of six SKUs has to be fully unpacked, sorted, and counted by hand. Mixed cartons are the most common cause of slow receiving and are frequently billed at a higher rate.

If you must ship a mixed carton — for example, the last partial box of a production run — label it clearly as mixed and itemize the contents on the outside.

3. Label every carton on the outside

Each carton should show the SKU, the quantity inside, and ideally the lot or batch number if your products carry one. Put the label where a receiver will see it without rotating the box.

4. Palletize if you are shipping freight

Cartons on a properly stretch-wrapped pallet unload in minutes. Loose floor-stacked cartons in a container take hours and often arrive damaged. Standard pallets, do not overhang the edges, and keep the stack stable.

5. Book the appointment

Most warehouses receive by appointment. Freight arriving without one can be refused or sit for days, and carriers may charge for the wasted trip. Confirm receiving hours and how much notice is required.

What documents does a 3PL need?

Send documents ahead of the shipment, not with it. A BOL discovered inside a sealed carton helps nobody.

How long should receiving take?

Dock-to-stock time — how long from arrival until inventory is sellable in your store — is the metric to hold your 3PL to. Ask for their committed dock-to-stock SLA and whether it differs for clean, single-SKU, labeled shipments versus mixed or unlabeled ones. It usually does, sometimes dramatically.

Two things you control that move this number more than anything the warehouse does: whether you sent an ASN, and whether cartons are single-SKU and labeled. Brands that get both right routinely see receiving completed in a fraction of the time.

What are the most common inbound mistakes?

1. No ASN. The shipment becomes a mystery to solve rather than a count to confirm.
2. Mixed cartons with no manifest. Every box has to be fully unpacked and sorted by hand.
3. Quantity mismatch between ASN and actual. Triggers a discrepancy hold, which pauses the whole receipt while it is investigated.
4. Barcodes that do not match the 3PL's SKU records. Common when a store SKU and a manufacturer part number differ. Reconcile them before shipping.
5. Shipping to the wrong address. Corporate offices and receiving docks are often different locations.
6. No appointment on a freight delivery. Refused delivery, redelivery fees, days lost.
7. Sending everything at once on the first shipment. Send a small test shipment first, confirm the flow works end to end, then send the bulk.

That last one is genuinely worth doing. A 200-unit test shipment surfaces barcode mismatches, label problems, and system integration issues while they are cheap to fix.

What about imported inventory going straight to a 3PL?

You can route a container directly from the port to your fulfillment center, which avoids double handling. A few things to confirm first:

• Can the facility receive containers? Not all can — some need the load transloaded to pallets first.
• Is the container floor-loaded or palletized? Floor-loaded is cheaper to ship and much more expensive to unload. Ask for the cost of each and compare the total.
• Who arranges drayage? The move from port to warehouse is a separate service from ocean freight.
• How long is free time before detention charges? A container waiting on a receiving appointment accrues fees fast.

Proximity to a port shortens the drayage leg and reduces detention exposure — one practical argument for a coastal node. See how East Coast fulfillment works and cross-docking explained if you want to skip storage entirely on fast-moving stock.

How much inventory should you send?

Enough to cover demand through your next replenishment lead time, plus safety stock — and no more. Over-sending inflates storage cost and raises your dead stock risk; under-sending causes stockouts. Our guides to calculating safety stock and preventing dead stock cover both sides of that.

If you are heading into Q4, send early. Receiving docks get congested in September and October, and dock-to-stock times stretch industry-wide at exactly the moment you need stock sellable.

How Atomix handles inbound

Inbound goes to your pod — the same dedicated space and consistent team that will pick and pack your orders. Practically, that means the people receiving your inventory are the people who will handle it every day, so barcode quirks and packaging details get learned once instead of rediscovered. You get a Pod Manager to book appointments and resolve discrepancies with directly, rather than a general receiving inbox.

For the full onboarding picture, see what happens after you sign with a 3PL and what to expect from a modern 3PL.

Frequently asked questions

What is an ASN in 3PL receiving?

An advance shipping notice — a document you send before inventory arrives listing the SKUs, quantities, carton or pallet count, expected arrival date, and carrier reference. It lets the warehouse verify a known shipment instead of investigating an unknown one.

Do I need barcodes on every unit before sending inventory to a 3PL?

Effectively yes. Scannable barcodes matching your SKUs are what make picking accurate. Most 3PLs will apply them for you as a billable per-unit service, but having your manufacturer do it is cheaper and faster.

Why does mixing SKUs in one carton slow receiving down?

A single-SKU carton can be verified in one scan. A mixed carton has to be opened, sorted, and counted unit by unit. Mixed cartons are the most common cause of long dock-to-stock times and often carry a higher receiving rate.

Can I ship a container directly to my fulfillment center?

Often yes, if the facility can receive containers. Confirm capability, whether the load is floor-loaded or palletized, who arranges drayage, and how much free time you have before detention charges begin.

How long does it take for inventory to become sellable?

Ask your 3PL for their dock-to-stock SLA. Clean shipments — ASN sent, single-SKU labeled cartons, palletized — receive substantially faster than mixed or unannounced ones.

What happens if the count does not match my ASN?

The receipt typically goes on a discrepancy hold while the variance is investigated, which delays the entire shipment becoming sellable. Accurate ASNs are the cheapest way to avoid this.

Getting ready to send your first shipment? Get a quote from Atomix and we will walk your team through inbound before anything ships.